Bluetooth BlueTooth - Allows users to make wireless connections between various communication devices such as mobile phones, desktop and notebook comp

Transcription

1 ECE 271 Week 8

2 Bluetooth BlueTooth - Allows users to make wireless connections between various communication devices such as mobile phones, desktop and notebook computers - Uses radio transmission - Point-to-multipoint (7-8) voice and data transmission - Uses spread spectrum, frequency hopping techniques (full-duplex signal at up to 1600 hops/sec) - Signal hops among frequencies at 1 MHz intervals and gives a high degree of interference immunity. - Short range applications (10 cms - 10 metres) - Operates in the 2.4GHz band - Gross data rate is 1 Mbps, actual data rates are 432 Kbps in full duplex (Time Division Duplex), 721/56 Kbps for asymmetric transmission and also 384 Kbps

3 Satellite Satellite - Microwave but not terrestrial - In some cases satellites can operate in the same frequency range as terrestrial systems - GEO (Geosynchronous Earth-Orbiting) satellites are positioned directly above the equator at altitudes of 35,786.1 km. GEOs maintain their positions relative to the Earth's surface - Orbital travel is in east-west direction. - GEOs are used for communication and weather forecast - LEO (Low Earth-Orbiting) satellites have altitudes of kilometres and mainly used in Remote Sensing applications. - LEOs have polar orbits (north-south direction, descending from north-south, ascending from south-north), with orbital speed of LEO satellites are 27,359 kilometres per hour - They can circle Earth in about 90 minutes. - MEOs (Middle Earth-Orbiting) are at at altitudes of km. - LEOs and MEOs do not maintain their relative positions.

4 Satellite - Satellites can transmit to, and receive from, a large area (foot print or coverage), thus advantageous in point-to-multipoint and broadcast applications. - Thousands of satellites exist in space among which around 500 of them are communication based satellites (mainly GEOs) - Similar to microwave systems, their performance varies with the weather condition - Propagation delay is quite important in satellite communications second delay from the transmitter to the receiver on earth - i.e 0.5 sec delay between the times when one communication point says Hello and hears the response Hello from the other communication point - For voice, videophone and some data applications (like games) this amount of delay is disturbing. - Transponder in the satellite includes: The receiving antenna to pick-up signals from the ground station Broadband receiver Input multiplexer and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink

5 Satellite - Telecommunication satellites receive signals from a ground station and send them down to another ground station located at a very long distance from the first (Relay action) - In the case of a long distance phone call or data transmission, communication can be two way - In the case of television broadcasts, the ground station's uplink is then downlinked over a wide region - Another application is in remote sensing where the satellite (equipped with cameras or various optical sensors) - In this case the satellite only downlinks data which is sensed from Earth s surface Atmosphere.

6 Satellite Ground Station - In the uplink or transmitting station, terrestrial data in the form of baseband signals is sent to the orbiting satellite by passing through: Baseband processor Up converter (frequency conversion) High powered amplifier Parabolic dish antenna - In the downlink, or receiving station, operation is reversed as compared to uplink.

7 Satellite Applications of Satellite Communications - Long distance telephone network among countries: International satellite consortium (Intelsat) - Television Broadcasting (Analog and digital): Direct free reception by home dishes (Free or scrambled channels) Terrestrial distribution after the satellite reception at the ground station - Automotive Navigation: Inmarsat applications as Global Positioning System GPS, Vehicle Tracking in a Fleet, Land Navigation as Maps in Cars, Maritime applications - VSAT (Very Small Aperture Terminal Networks)

8 Transmission Media Microwave - Receive/transmit home/office small antenna aperture terminals connecting to a central hub via satellite - Antenna dish diameter around meter - Operates in the Ku-band (around 14 GHz uplink, 11 GHz downlink) and C- band (around 6 GHz uplink, 4 GHz downlink) frequencies - Ku-band requires smaller antenna diameter than C-band - Can have Bi-Directional Operation (uplink and downlink) or Receive-Only Operation (downlink) - Multipoint network providing two-way data, voice and multi-media transmission - Can provide internet downloads at up to 2 Mbps - Star-network that connects one or more main sites to various remote sites - Uses TDMS (Time Division Multiple Access) as the means to send data to each remote site

9 GEO (Geosynchronous Earth-Orbiting) satellites above VSAT the equator at altitudes of 35,786.1 km altitude MEO (Middle Earth-Orbiting) satellites at altitudes of km LEO (Low Earth- Orbiting) satellites have altitudes of kilometres L-Band ( MHz) 800 MHz range Little LEOs (Below 1 GHz) Kbps. Messaging, paging, vehicle location 2 GHz range Voice (Cellular) C-Band (UL around 6 GHz, DL around 4 GHz) Commercial TV Broadcast, Digital Radio, VSAT Mobile Big LEOs (Above 1 GHz) Mobile Kbps. Voice (Cellular) Ku-Band (Uplink around 14 GHz, Downlink around 11 GHz) Up to 155 Mbps global area data communications, Most of the Current Commercial Analog/Digital TV Broadcast, Digital Radio, VSAT Up to 155 Mbps regional area data communications, Analog/Digital TV Broadcast, Digital Radio Ka-Band (Uplink around 30 GHz, Downlink around 20 GHz) Up to 155 Mbps data, Multimedia, Military Applications, High speed internet access, tele-education, telemedicine, ATM based services including wide area networks and local area network interconnection, videotelephony, cheap videoconferencing, television services to aircraft, local television, rural telephony, satellite newsgathering, alternative to VSAT networks, remote monitoring Broadband LEOs Mbps Data, Multimedia

10 Transmission Media Microwave Remark RSL does not account for antenna alignment errors or path fading phenomena, such as multipath reflections, signal distortions, variable atmospheric conditions, and obstructions in the path. Link Feasibility Formula To determine if a link is feasible, compare the calculated Receive Signal Level with the Receiver Sensitivity Threshold. The link is theoretically feasible if RSL R x If the Receive Signal Level Receiver Sensitivity Threshold, then the link may be feasible since the signal should be strong enough to be successfully interpreted by the receiver In the above LINK-1 Example, link is feasible since 58.9 dbm is greater than 77 dbm In the above LINK-2 Example, the link is feasible since dbm is greater than -81 dbm.

11 MMDS MMDS Multichannel Multipoint Distribution Service, also known as cableless Cable-TV TV Signals from satellite or other sources received and retransmitted by microwave Material to be delivered over MMDS are satellite, terrestrial and cable delivered programs, local baseband services MMDS channels transmitted from an omni-directional antenna (or doughnut pattern) - radiates equal in all directions in a chosen plane Range is around 50 km Only 200 MHz (between 2.5 GHz and 2.7 GHz) allocated to MMDS For TV signals with 6 MHz bandwidth, there are only 33 channels in MMDS

12 LMDS Local Multipoint Distribution Services (LMDS) Deploying a fixed link for broadband network access to customers premises is difficult and expensive Provides wireless broadband Consists of a transmitter which sends signals on a combination of channels to numerous receivers such as homes and businesses (i.e it is a point to multipoint system) Operates in various frequency bands, from 24GHz to 38GHz Compared to MMDS, LMDS can have broader bandwidth But coverage is limited (around 5 km) and components are more expensive Network coverage is increased by connecting the existing carrier network to a Base Transceiver Station (BTS) through a Customer Interface Point This connection is extended, using high frequency radio transmission, to an antenna located at the customer s premises i.e. LMDS provides wireless broadband connection between the carrier s network and its customers

13 LMDS LMDS applications LMDS provides digital two-way voice, high speed Internet access and data and video services LMDS offers the service providers and ISPs last mile connectivity between their fixed networks and customer sites LMDS connects LANs, intranets and PBXs of companies with distributed offices LMDS can provide 10 Mbps or faster connections which is attractive to customers who are using E1/T1 leased line connections between their LANs or to their ISP LMDS uses up to 622Mbps by allocating a large spectrum ( MHz) to a single subscriber or usually 10 Mbps for each subscriber in order to maximise the number of subscribers

14 LMDS LMDS link separation Two ways of separating the uplink connection (from the subscriber to the base station) from the downlink connection (from the base station to the subscriber) In Time Division Duplexing (TDD), the subscriber and the base station take turns talking to each other. At any time, both parties will use the entire spectrum allocated for that link In Frequency Division Duplexing (FDD), the uplink and the downlink use different frequency bands separated by a large guard band (e.g. a separation of 1008MHz for the GHz band) to avoid interference Since one base station needs to communicate with several sets of Consumer Premises Equipment (CPE), there is need to partition

15 LMDS LMDS link separation The uplink or the downlink frequency band (for the FDD case) among all the subscribers served by the base station The uplink or the downlink transmission duration (for the TDD case) among all the subscribers served by the base station In Frequency Division Multiple Access (FDMA), each CPE is allocated a small slice of the spectrum allocated to the uplink or downlink, and transmits simultaneously along with the other CPEs, i.e. different user transmissions are separated in frequency Time Division Multiple Access (TDMA) approach separates the transmissions to the various CPEs in time such that at any instance the base station communicates with only one CPE, i.e. different user transmissions are separated in time

16 WLL Wireless Local Loop (WLL) Makes PSTN service possible in a wireless environment Can be based on CDMA Connected directly to the telephone exchange Operates in wide range of frequency bands Covers an area of diameter bigger than 15 km Supports up to 56 kb/s modems or digital data rates of 64 kb/s or 128 kb/s Provides wireless Internet access

17 Wireless Local Area Networks (WLAN) WLAN: Operates at 900 MHz or in the microwave range ( MHz, MHz, MHz) Data rates of 22Mbps, 54 Mbps Alternative to the traditional LANs based on twisted pair, coaxial cable, and optical fiber Used for the same applications as wired or optical LAN More flexible because moving a wireless node is easier Best fit for portable computers Can be used in combination with cabled LANs

18 Wireless Local Area Networks (WLAN) WLANs use three types of transmission techniques: 1. Spread Spectrum Technology Currently the most widely used transmission technique for WLANs In spread-spectrum more than essential bandwidth is used to achieve reliability and security If a receiver is not tuned to the right frequency, a spreadspectrum signal looks like background noise Two types of spread spectrum radio: frequency hopping and direct sequence

19 Wireless Local Area Networks (WLAN) Direct-Sequence Spread Spectrum Technology (DS-SS) Most wireless spread-spectrum LANs use DS-SS DS-SS generates a redundant bit pattern for each bit to be transmitted This bit pattern is called a spreading code Each bit in this code is called a chip Receiver should know transmitter's spreading code to decipher data This spreading code is what allows multiple direct sequence transmitters to operate in the same area without interference Once the receiver has all of the data signal, it uses a correlator to remove the chips and bring the signal to its original length To an unintended receiver, DS-SS appears as low-power wideband noise and is rejected (ignored) by most narrowband receivers

20 Wireless Local Area Networks (WLAN) Frequency-Hopping Spread Spectrum (FH-SS) Uses a narrowband carrier that changes frequency in a code pattern known to both transmitter and receiver A receiver, hopping between frequencies in synchronization with the transmitter, receives the message The message can only be fully received if the series of frequencies are known Since only the intended receiver knows the transmitter's hopping sequence, only that receiver can receive all the data To an unintended receiver, FH-SS appears to be short-duration impulse noise.

21 Wireless Local Area Networks (WLAN) 2. Narrowband WLAN: Similar to broadcasting from a radio station User tunes both the transmitter and the receiver to a certain frequency. Does not require line-of-sight focusing However, because the signal is high frequency, it is subject to attenuation from steel and load-bearing walls. 3. Infrared WLAN (IR WLAN) IR WLAN is high bandwidth Two systems: Line-of-sight (LOS) or diffuse systems LOS IR: Major disadvantage is that signal can easily be obstructed, LOS are limited in range (a few meters) Most familiar LOS infrared communication device is the TV remote control A connection is made by transmitting data using two different intensities of infrared light to represent the 1s and 0s The infrared light is transmitted in a 30-degree cone giving some flexibility in orientation of the equipment, but not much.

22 Wireless Local Area Networks (WLAN) 2. Diffuse IR: Diffuse IR WLAN does not require line-of-sight but their use is limited within a single room Diffuse IR operates by flooding an area with infrared light, in much the same way as a conventional light bulb illuminates a room IR signal bounces off the walls and ceiling so that a receiver can pick up the signal regardless of orientation Diffuse IR is a compromise between LOS infrared and radio technology. It combines the advantages of high data rates from infrared and the freedom of movement from radio However, even though its speed is up to 4Mbits/s, it is shared among all the users, unlike LOS infrared Although people can enjoy its speed and its mobility, it is restricted within a certain range, such as a room. It doesn t go through a wall.

23 Wireless Local Area Networks (WLAN)